Lighting device with switching material

ABSTRACT

A lighting device comprises a light-emitting module with light-emitting elements, wherein the light-emitting elements are arranged adjacent to each other and are configured to emit light towards a light-emitting side. The light-emitting module is configured such that the light-emitting elements can be addressed partially independently of each other, such that some may be brought into a switched-on state while others are brought into a switched-off state. A top layer is disposed on the light-emitting module at the light-emitting side. Further comprising a switching material capable of a reversible change in transmittance for the light emitted by changing to a higher transmittance in regions where the top layer situated on light-emitting elements in the switched-on state or to a lower transmittance in regions of the top layer situated in the switched-off state. The invention further refers to methods for producing and operating a lighting device and using a lighting device.

FIELD OF INVENTION

The present disclosure relates to lighting devices comprising alight-emitting module, wherein light-emitting elements such as lightemitting diodes (LEDs) are arranged adjacent to each other and areconfigured to be addressed independently of each other.

BACKGROUND

Lighting devices may comprise an arrangement of multiple light-emittingelements, for example LEDs or LED packages. For some applications,so-called “segmented LEDs” have been proposed, wherein the LEDs areconfigured to be addressed at least partially independently of eachother in that some LEDs may be brought into a switched-on state whileother LEDs remain in a switched-off state. That is, segments of thelighting device may be activated while other segments are inactive. Withthis, the total intensity of the light emitted by the lighting devicecan be varied, as well as the shape of light and the intensitydistribution. In case LEDs with different colors are used, the segmentedLEDs may also provide a variation in color for the emitted light.

Light-emitting elements such as LEDs typically have a certain amount oflateral light diffusion. While a light-emitting element may beconfigured to emit the light substantially in one direction, e.g. from alight-emitting side or face, part of the light is also emitted towardsother directions. Light-emitting elements such as LEDs or LED packagesare also usually provided with architectures that comprise elements likesubstrates, wavelength conversion elements, and diffusing layers. Sucharchitectures may lead to a scattering of light emitted by the LED awayfrom the light-emitting side and therefore increase the amount oflateral light diffusion.

Lateral light diffusion may in particular become problematic whenlight-emitting elements are arranged adjacent to each other, forinstance in segmented LEDs. In case the segmented LED is only partiallyactivated, light from active segments may reach inactive segments.Therefore, light not only appears from the active segments, but alsoappears with lesser intensity from neighboring, inactive segments. As aresult, a “leaking” of light or undesired cross talk between thesegments appears, reducing the intensity contrast of the lightingdevice. When light conversion elements are provided, the lightconversion elements of inactive segments may be illuminated by theactive segments, leading to undesired color differences between thesegments. In segmented LEDs comprising segments providing differentcolors, a loss in color contrast can also occur.

A possibility to reduce the loss in contrast due to lateral lightdiffusion is to provide reflective elements in between the individuallight-emitting elements or the individual segments. However, suchreflective elements usually restrict the spacing between thelight-emitting elements in that the light-emitting elements have to bearranged with a certain minimum distance to accommodate the reflectiveelements. In addition, the production costs are increased, as additionalelements need to be incorporated into the lighting device.

WO 2017/134589 A1 discloses a coating comprising vanadium oxide dopedwith one or several elements and at least germanium.

U.S. Pat. No. 9,857,049 B2 relates to an LED illumination device with acarrier structure, a suspension structure, and a light-emittingstructure.

WO 2017/104313 A1 describes an optical film which contains vanadiumdioxide containing particles, wherein the near-infrared shielding rateis adjusted in accordance with the temperature environment.

U.S. Pat. No. 9,117,776 B2 relates to an organic light-emitting displaywith a color-changing material layer provided on a display panel.

U.S. Pat. No. 9,431,635 B2 describes a light-emitting componentincluding an electrically active region with an organic functional layerstructure. A thermotropic layer is arranged outside the electricallyactive region.

SUMMARY

It is an object of the present invention to provide a lighting devicewith light-emitting elements that can be addressed independently of eachother, which enhances the contrast of the illumination betweenlight-emitting elements in a switched-on state and light-emittingelements in a switched-off state. The invention further relates to amethod for producing such a lighting device and a use of such a lightingdevice based on the aforementioned object.

According to a first aspect of the present invention, a lighting deviceis provided, comprising: an light-emitting module with light-emittingelements, wherein the light-emitting elements are arranged adjacent toeach other and are configured to emit light towards a light-emittingside, wherein the light-emitting module is configured such that thelight-emitting elements can be addressed at least partiallyindependently of each other in that some of the light-emitting elementsmay be brought into a switched-on state while other light-emittingelements may be brought into a switched-off state; and a top layerdisposed on the light-emitting module at the light-emitting side,wherein the top layer comprises a switching material capable of areversible change in transmittance for the light emitted by thelight-emitting elements, and wherein the top layer is configured tochange to a higher transmittance in regions of the top layer situated onlight-emitting elements in the switched-on state compared to atransmittance in regions of the top layer situated on light-emittingelements in the switched-off state.

According to a second aspect of the present invention, a method forproducing a lighting device is provided, in particular the lightingdevice according to the first aspect, the method comprising: providing alight-emitting module by arranging light-emitting elements adjacent toeach other such that the light-emitting elements emit light towards alight-emitting side, wherein the light-emitting module is configuredsuch that the light-emitting elements can be addressed independently ofeach other in that some of the light-emitting elements may be broughtinto a switched-on state while other light-emitting elements may bebrought into a switched-off state; providing a top layer, wherein thetop layer comprises a switching material capable of a reversible changein transmittance for the light emitted by the light-emitting elements;and disposing the top layer on the light-emitting module at thelight-emitting side, wherein the top layer is configured to change to ahigher transmittance in regions of the top layer situated onlight-emitting elements in the switched-on state compared to atransmittance in regions of the top layer situated on light-emittingelements in the switched-off state.

According to a third aspect of the present invention, a method foroperating a lighting device according to the first aspect is provided,the method comprising: bringing some of the light-emitting elements intoa switched-on state while bringing other light-emitting elements into aswitched-off state; and changing the top layer to a higher transmittancein regions of the top layer situated on light-emitting elements in theswitched-on state compared to a transmittance in regions of the toplayer situated on light-emitting elements in the switched-off state.

According to a fourth aspect of the present invention, a use of alighting device according to the first aspect is provided as cameraflash light or in automotive lighting, in particular as automotiveheadlight.

Exemplary embodiments of the first, second, third, and fourth aspect ofthe invention may have one or more of the properties described below.

The light-emitting module may comprise an arrangement of light-emittingelements, wherein the light-emitting elements are arranged adjacent toeach other. In particular, an array of light-emitting elements isprovided, for example a one-dimensional or 1×N array, in that multiplelight-emitting elements are arranged adjacent to each other along onedirection. The light-emitting elements may also be arranged astwo-dimensional array with light-emitting elements being arrangedadjacent to each other on a surface or a plane, for instanceconfigurations like 3×3 or 3×2 arrays of light-emitting elements. Arraysof light-emitting elements may also be larger, e.g. arrays of 3×7 or5×40 light-emitting elements are possible, in particular for automotiveapplications. Arrays of light-emitting elements may be regular in thatthe distances between neighboring light-emitting elements are similar.Arrays of light-emitting elements may also comprise light-emittingelements of different sizes, e.g. with different segments being formedof light-emitting elements of different sizes.

Under the light-emitting elements being arranged “adjacent to eachother”, it may be understood that each light-emitting element is broughtclose enough to another light-emitting element so that a cross-talkbetween light-emitting elements due to lateral light diffusion issubstantial. In particular, the minimal distance between light-emittingelements may be in the same order of magnitude or less than thedimension of a light-emitting face of the light-emitting elements. Forinstance, the dimensions of the light-emitting face of thelight-emitting elements, in particular LEDs may be in the order ofmillimeters, and in particular 1 mm² to 100 mm², for example about 1.5mm×1.5 mm. The distances between neighboring light-emitting elements maybe less than 1 mm, in particular less than 0.5 mm. In some embodiments,at least part of the light-emitting elements may be arranged such thatside faces of the light-emitting elements are in direct contact or abutto each other.

The light-emitting elements are arranged such that the light-emittingelements emit light towards a light-emitting side. For example, thelight-emitting elements have a light-emitting face, with thelight-emitting faces of several light-emitting elements in thelight-emitting module facing substantially in the same direction. Inparticular, the light-emitting elements of the light-emitting module arearranged substantially on the same surface, for example on the samesubstrate, and may in particular be arranged in the same plane.

The light-emitting elements may in particular comprise at least onesemiconductor element capable of light emission. In particular, at leastone light-emitting element may comprise at least one LED. LEDs maycomprise at least one semiconductor element such as a p-n-junction, adiode, and/or a transistor. For instance, the LEDs may be provided inform of separate or combined LED dies and/or LED packages, whereinparticular at least one LED may be arranged on a substrate, e.g. asapphire substrate. An LED package may comprise a wavelength conversionelement (e.g. based on phosphor) and/or may comprise at least oneoptical element such as a diffusing layer, a diffractive element (e.g. alens) and/or a reflective element (e.g. a reflector cup). The LED orLEDs may for instance be integrated into an LED lead frame. The LEDs arein particular based on inorganic compounds. In other embodiments, theLEDs may be based on organic compounds, for instance in the form ofOLEDs. In some embodiments, different types of LEDs providing differentcolors are used.

The light-emitting elements may also be based on other light sourcessuch as lasers. For instance, lasers can be used, in particular to pumpwavelength conversion elements (e.g. based on phosphor) with light.Lasers may for instance be based on laser diodes or edge-emittinglasers. In particular, vertical-cavity surface-emitting lasers (VCSEL)may be used, such as VCSEL arrays.

The light-emitting elements are configured to be addressed at leastpartially independently of each other in that some of the light-emittingelements may be brought into a switched-on state while otherlight-emitting elements are brought into a switched-off state.Therefore, the lighting device may provide an illumination in segmentsof light-emitting elements, wherein the illumination can be varied bybringing different segments of light-emitting elements into theswitched-on state. “Bringing” into a switched-off state or switched-onstate may also mean that the current state of an light-emitting elementis maintained, while the state of at least one other light-emittingelement is changed.

The light-emitting module in particular comprises electrical contactsfor the light-emitting elements and electrical conduction elements, e.g.wiring and/or printed circuit boards for providing a contact of thelight-emitting elements to a power source. The electrical contacts forthe light-emitting elements and/or electrical conduction elements may beconfigured such that at least part of the light-emitting elements can beaddressed independently, i.e. at least part of the light-emittingelements can be provided with energy independently from each other. Insome embodiments, the lighting device may comprise control means forcontrolling the independent addressing of the light-emitting elements.In some embodiments, light-emitting elements may be grouped, wherein thegroups of light-emitting elements may be addressed independently of eachother. In other embodiments, all of the light-emitting elements of thelight-emitting module are configured to be addressed independently ofeach other.

Light-emitting elements that are configured to be addressedindependently of each other may be provided based on separatecomponents, e.g. separate semiconductor elements such as separate LEDsand/or separate LED packages. In other embodiments, at least some of thelight-emitting elements are formed together in a monolithic element,e.g. a monolithic semiconductor element like a monolithic LED die withindependently addressable segments. “Light-emitting elements” may inthis sense also refer to an (e.g. monolithic) element that is capable ofemitting light from sections that can be addressed independently of eachother.

A top layer is disposed on the light emitting module at thelight-emitting side, such that the light emitted by the light-emittingelements, in particular by a light-emitting face of the light-emittingelements, at least partially passes the top layer for illumination whenthe lighting device is activated.

As the top layer comprises a switching material capable of a reversiblechange in transmittance for the light emitted by the light-emittingelements, the contrast between light-emitting elements in theswitched-on state and light-emitting elements in the switched-off statecan be enhanced. With the switching material, the top layer isconfigured to change to a higher transmittance in regions of the toplayer situated on light-emitting elements in the switched-on statecompared to a transmittance in regions of the top layer situated onlight-emitting elements in the switched-off state. That is, thetransmission of light in regions of the top layer situated onlight-emitting elements in the switched-off state is effectively reducedor blocked compared to regions of the top layer situated onlight-emitting elements in the switched-on state. Therefore, lightleaking from light-emitting elements in the switched-on state tolight-emitting elements in the switched-off state, e.g. by lateral lightdiffusion caused by lateral emission, total internal reflection insidethe elements (e.g. an effective light guiding in a layered structure ofthe light-emitting elements) and/or scattering, is at least partiallyblocked at the top layer in the regions of the light-emitting elementsin the switched-off state. As a result, a transmission of light mostlyoccurs in the regions of the top layer on light-emitting elements in theswitched-on state.

The transmittance of the top layer may in particular be understood asthe fraction of incident light transmitted through the top layer. Theincident light may be the light emitted by the light-emitting elementimpinging on a first side of the top layer, with part of the light beingtransmitted to a second side of the top layer opposite of the firstside. The transmission may be understood as total transmittance, i.e.the ratio of incident electromagnetic energy that is not absorbed,scattered or reflected such that it is transmitted. For example, theswitching material may be capable of a reversible change in thescattering of light, in the color of the transmitted light, and/or inthe absorption of light, e.g. a change from black to transparent ortranslucent.

In particular, when the transmittance is measured in percent (with 0%corresponding to no electromagnetic energy of an light-emitting elementpassing the top layer and 100% corresponding to all electromagneticenergy of an light-emitting element passing the top layer), the toplayer may be configured to change transmittance by at least 10%, inparticular by at least 30%. In some embodiments, the top layer may beconfigured to change transmittance by at least 70%, in particular by atleast 80%.

In an exemplary embodiment of the invention, the regions of the toplayer situated on light-emitting elements in the switched-on state havetranslucent properties. In particular, the switching material may beconfigured for a reversible change from substantially opaque propertiesto translucent properties. With the translucent properties of theregions of the top layer, the light emitted by the light-emittingelements in the switched-on state and transmitted through the top layeris scattered to obtain a more diffuse and softer illumination. In someembodiments, one or more additional diffusion layers on thelight-emitting elements such as LEDs and/or LED packages can thereforebe omitted, simplifying the production of the lighting device.

In another exemplary embodiment of the invention, the switching materialcomprises at least one thermochromic material. Thermochromic materialsmay change transmittance depending on temperature, such that thetransmittance of the regions of the top layer may be changed based on avariation of temperature. In particular, thermochromic materials may beconfigured to increase transmittance with increasing temperature.Regions of the top layer on light-emitting elements in the switched-onstate may therefore be configured to be heated and/or regions of the toplayer on light-emitting elements in the switched-off state may beconfigured to be cooled to change the transmittance.

A heating and/or cooling of regions may be active in the sense thatheating means and/or cooling means are provided, which are capable ofcontrolling the temperature of regions of the top layer. The heatingmeans and/or cooling means may be controlled together with theaddressing of the light-emitting elements, for example by control means.A heating of regions may also be passive in the sense that waste heat ofother elements of the lighting device is used.

In particular, the light-emitting elements in the switched-on state mayproduce heat and transfer heat to the top layer in the correspondingregions. The light-emitting elements may transfer heat by convection tothe top layer. Heat conduction elements may also be provided, forexample in that heat sinks of the light-emitting elements are connectedto the top layer. In particular when LEDs are used as light-emittingelements, a substantial waste heat may be produced that can be used toprovide heat to the top layer. LEDs with wavelength conversion elementssuch as white LEDs comprising phosphor layers may produce a suitableamount of heat due to the conversion of higher photon energies to lowerphoton energies.

In an exemplary embodiment of the invention, the at least onethermochromic material is configured to increase transmittance attemperatures corresponding to an operating temperature of thelight-emitting elements. For example, the temperature range in which thetransmittance of the thermochromic material has the highest change maycorrespond to the temperature range of the top layer caused by theoperation of the light-emitting elements. With this, the change intransmittance can be induced by the waste heat of the light-emittingelements themselves such that the top layer automatically changes thetransmittance in regions to enhance the contrast. Typical temperatureranges depend on the application and the overall heatsinking of thelighting device. The temperature range particularly suitable forapplications like camera flash or other application requiring highercurrents may be 100° C. to 250° C., in particular 150° C. to 230° C.Other applications may work at lower temperatures, e.g. 50° C. to 150°C.

In another exemplary embodiment of the invention, the at least onethermochromic material comprises at least one leuco dye and/or at leastone metal oxide. At least one leuco dye can be chosen from a group ofdyes based on triphenyle methane, sulfur dyes, and indigo dyes. Dyesbased on triphenyle methane may comprise such dyes as aniline green,malachite green, and/or china green. Sulfur dyes may in particular beobtained from aromatic compounds reacted with sodium polysulfide, e.g.sulfur black, sulfur blue, and sulfur yellow. Indigo dyes may beobtained from natural sources. A further type of leuco dye asthermochromic material is crystal violet lactone leuco dye (CVL).

Metal oxides may also have thermochromic properties, and in particulartransition metal oxides such as VO₂ may be used.

Different types of thermochromic materials may be combined for the toplayer, e.g. a mixture of different leuco dyes, to obtain a high changein transmittance in a suitable temperature range, a certain color forthe top layer, and/or translucent or transparent properties of the toplayer.

In another exemplary embodiment of the invention, the switching materialcomprises at least one electrochromic material. The top layer may beconfigured such that voltage may be applied to regions of the top layerto change transmittance by means of the at least one electrochromicmaterial.

In an exemplary embodiment of the invention, the at least oneelectrochromic material is configured to change to a highertransmittance when a voltage is applied to the top layer. Hence, voltagemay be applied to the regions of the top layer on the light-emittingelements in the switched-on state to provide a higher contrast and toavoid cross-talk of the light-emitting elements. Conversely, the atleast one electrochromic material may be configured to change to a lowertransmittance when a voltage is applied to the top layer. Voltage may beapplied to the regions of the top layer on the light-emitting elementsin the switched-off state or at least to regions of the top layeradjacent to the regions of the top layer on the light-emitting elementsin the switched-on state. In particular, connection elements forproviding the light-emitting elements with electrical energy may also beconnected to the top layer, and provide a voltage to correspondingregions of the top layer.

In another exemplary embodiment of the invention, the at least oneelectrochromic material comprises at least one selected from a groupcomprising metal oxides, metal hydroxides, viologens, conjugatedpolymers, metal coordination complexes, metal hexacyanometallates, andmetal pthalocyanines. Electrochromic metal oxides can for example bechosen from a group of WO₃, NiO, MoO₃, V₂O₅, and Nb₂O₅. An example for ametal hydroxide is Ir(OH)₃. The electrochromic material may for examplebe based on viologens such as polymeric viologens, ethyl viologen,heptyl viologen, and/or (vinyl) benzyl viologen. As conjugated polymer,in particular conjugated conducting polymers may be used, for examplepolypyrrole, polythiophene, and/or polyaniline (PANI). Metalcoordination complexes and/or metallopolymers may include Mo, Fe, Ru, Oscomplexes in particular based on pyridines. Metal hexacyanometallatesmay comprise Prussian blue and/or Ruthenium purple. Examples for metalpthalocyanines are [Lu(Pc)₂] and Co(II) pthalocyanine.

In another exemplary embodiment of the invention, the switching materialis encapsulated. For example, switching material like leuco dyes may beencapsulated and in particular microencapsulated. For instance, capsuleswith an inner section containing the switching material and an outersection comprising a protective material may be provided. The switchingmaterial may be encapsulated in capsules with an average dimension of 1μm to 50 μm, in particular 5 μm to 10 μm. Capsules may be substantiallyspherical. It also possible that the switching material, e.g. leucodyes, are encapsulated by disposing the switching material into a porousstructure. Encapsulated switching material may in particular beintegrated into the top layer. In addition or as an alternative,switching material may be provided as a coating on the top layer. Acoating comprising switching material is applied on one or both sides ofthe top layer. A coating may be applied as a slurry, powder,solvent-based ink, resin such as a silicone, and/or based on a masterbatch comprising the switching material.

In an exemplary embodiment of the invention, the switching material iscapable of a reversible change in light scattering for the light emittedby the light-emitting elements. In an exemplary embodiment, theswitching material may comprise a porous structure, the porous structurecomprising: a non-light absorbing material structure comprising aplurality of sub-micron pores; and a polymer matrix, wherein the polymermatrix fills the plurality of sub-micron pores, creating an interfacebetween the non-light absorbing material structure and the polymermatrix, a refractive index of the non-light absorbing material structureis different than a refractive index of the polymer matrix at a firsttemperature, a refractive index difference between the refractive indexof the non-light absorbing material structure and the refractive indexof the polymer matrix is such that the plurality of sub-micron poreswithin the optically functional porous structure has a light scatteringability at the first temperature, and the refractive index differencebetween the refractive index of the non-light absorbing materialstructure and the refractive index of the polymer matrix decreases at asecond temperature, such that the light scattering ability of theplurality of sub-micron pores decreases. The polymer matrix may inparticular be based on silicone.

With the refractive index of the polymer matrix being greater than therefractive index of the non-light absorbing material structure, a lightscattering effect occurs at the interface between the two materials. Asthe temperature changes to the second temperature, the refractive indexof the polymer matrix decreases such that the refractive indexdifference between the non-light absorbing material, which outlines theshape of the sub-micron pores, and that of the polymer matrix, whichfills the sub-micron pores, decreases thereby resulting in decreased tono light scattering by the sub-micron pores-dielectric surfaceinterface. Hence, corresponding porous structures may provide areversible change in transmittance and may be used as switchingmaterial.

In particular, the refractive index of the non-light absorbing materialstructure is less than the refractive index of the polymer matrix at thefirst temperature, and the second temperature is greater than the firsttemperature, such that for instance waste heat of the light-emittingelements may induce a reduction in scattering and therefore an increasein transmittance.

In an exemplary embodiment of the invention, the switching materialcomprises porous silica. In particular, the non-light absorbing materialstructure of a porous structure is formed from porous silica. Thenon-light absorbing material structure may form a plurality ofmicron-sized porous particles dispersed throughout the porous structure,wherein the plurality of sub-micron pores are located within theplurality of micron-sized porous particles. The plurality ofmicron-sized porous particles may for instance have a diameter of 10 μmto 50 μm. Each sub-micron pore of the plurality of sub-micron pores mayhave an internal diameter of 50 nm to 400 nm.

In some embodiments, the non-light absorbing material structure forms amesh slab comprising an interconnected network of the plurality ofsub-micron pores. The porous structure may also further comprise airvoids, wherein a space occupied by the air voids decreases as thepolymer matrix thermally expands, decreasing light scatter, and thespace occupied by the air voids increases as the polymer matrix shrinks,increasing light scatter.

In other embodiments with the switching material being capable of areversible change in light scattering, the switching material maycomprise scattering elements based on MgF₂, wherein the scatteringelements in particular be embedded in a matrix material, e.g. a matrixmaterial based on dimethylsilicone.

In another exemplary embodiment of the invention, the light-emittingmodule further comprises at least one light-blocking element arrangedbetween the light-emitting elements. The at least one light-blockingelement may be configured as reflective or absorbing element in betweenthe light-emitting elements to further reduce the amount of lightleaking from light-emitting elements in the switched-on state tolight-emitting elements in the switched-off state.

In some embodiments of the invention, the lighting device is configuredas camera flash light. In particular in adaptive flash lighting,addressing different segments of light-emitting elements such assegments of LEDs independently may be used for an optimizedillumination. For instance, the lighting device may be used in the fieldof photography to provide additional lighting with a variablebrightness. In automotive lighting and in particular as automotiveheadlight, the lighting device may be used for a variable illumination.With the lighting device according to the invention, the illuminationmay be optimized for high visibility while reducing the risk of glaring.

When operating the lighting device according to the invention, some ofthe light-emitting elements may be brought into a switched-on state,i.e. certain segments are addressed. The remaining light-emittingelements may be kept in or brought into a switched-off state, such thata segmented illumination with a contrast between active and inactivesegments is obtained. The top layer may be changed to a highertransmittance in regions of the top layer situated on light-emittingelements in the switched-on state compared to a transmittance in regionsof the top layer situated on light-emitting elements in the switched-offstate. The change in transmittance of the top layer may be active, forinstance by application of voltage to a top layer comprisingelectrochromic materials. The change in transmittance may also beinduced by the light-emitting elements, for instance by means of wasteheat that induces a change in transmittance of a top layer comprising atleast one thermochromic material.

The features and example embodiments of the invention described abovemay equally pertain to the different aspects according to the presentinvention. In particular, with the disclosure of features relating tothe lighting device according to the first aspect, also correspondingfeatures relating to the methods according to the second and thirdaspect and to the use according to the fourth aspect are disclosed.

It is to be understood that the presentation of embodiments of theinvention in this region is merely exemplary and non-limiting.

Other features of the present invention will become apparent from thefollowing detailed description considered in conjunction with theaccompanying drawings. It is to be understood, however, that thedrawings are designed solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims. It should be further understood that thedrawings are not drawn to scale and that they are merely intended toconceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with referenceto the accompanying drawing, in which:

FIG. 1 shows a schematic representation of a lighting device from a sideview;

FIG. 2 shows a schematic representation of the lighting device of FIG. 1from a top view;

FIG. 3 shows a schematic representation of a first embodiment of alighting device according to the invention from a side view;

FIG. 4 shows a schematic representation of the first of embodiment ofthe lighting device from a top view;

FIG. 5 shows a schematic representation of the first of embodiment ofthe lighting device with a different state of the light-emittingelements from a side view; and

FIG. 6 shows a schematic representation of the first of embodiment ofthe lighting device with a different state of the light-emittingelements from a top view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic representation of a lighting device 2 from aside view. LEDs 4 a-4 c are arranged adjacent to each other on asubstrate 6 and are configured to emit light towards a light-emittingside 8. The lighting device 2 is also shown in FIG. 2 from a top view.The LEDs 4 a-4 c are forming a segmented LED module and can be addressedindependently of each other in that some of the LEDs 4 a-4 c may bebrought into a switched-on state while other LEDs 4 a-4 c are broughtinto a switched-off state. In FIGS. 1 and 2, LED 4 b is in theswitched-on state and emits light as indicated by the arrows 10, whileLEDs 4 a and 4 c are in the switched-off state and inactive.

The LEDs 4 a-4 c are affected by lateral light diffusion, as lightemitted by the LEDs 4 a-4 c is not only emitted towards the lightemitting side 8, but may also be laterally emitted, reflected and/orscattered away from the light-emitting side 8. As the LEDs 4 a-4 c arearranged adjacent to each other, light may leak from active segments toinactive segments. As a consequence, light 10 appears not only as beingemitted from the LED 4 b in the switched-on state. Also parts of theinactive LEDs 4 a and 4 c appear illuminated with light 12. Therefore, alight cross talk or color over between the LEDs 4 a-4 c occurs, reducingthe contrast of the lighting device 2.

FIG. 3 shows a schematic representation of a lighting device 14according to the invention from a side view. FIG. 4 shows thecorresponding top view. A light-emitting module with light-emittingelements 16 a-16 c and a substrate 18 is provided. The light-emittingelements 16 a-16 c are arranged adjacent to each other on the substrate18, such that the light-emitting elements 16 a-16 c are configured toemit light towards a light-emitting side 20. The light-emitting moduleis configured such that the light-emitting elements 16 a-16 c can beaddressed independently of each other in that some of the light-emittingelements 16 a-16 c may be brought into a switched-on state while otherlight-emitting elements 16 a-16 c may be brought into a switched-offstate. For example, each light-emitting element 16 a-16 c has electricalconnection elements (not shown) that allow for an independent supplywith electrical energy and therefore an independent activation of thelight-emitting elements 16 a-16 c. The light-emitting elements 16 a-16 cmay comprise LEDs and/or LED packages. The light-emitting module maytherefore represent a segmented LED module in that segments of LEDs maybe addressed independently. In FIGS. 3 and 4, light-emitting element 16b is in the switched-on state and emits light as indicated by the arrows22, while light-emitting elements 16 a and 16 c are in the switched-offstate and are inactive.

A top layer 24 is disposed on the light-emitting module at thelight-emitting side 20, wherein the top layer 24 comprises a switchingmaterial capable of a reversible change in transmittance for the lightemitted by the light-emitting elements 16 a-16 c. As described above inconjunction with FIGS. 1 and 2, lateral light diffusion occurs and lightemitted by the light-emitting element 16 b is not only emitted towardsthe light emitting side 20, but is also emitted laterally, reflected,and/or scattered away from the light-emitting side 20. Light maytherefore leak to the inactive light-emitting elements 16 a, 16 c andparts of the inactive light-emitting elements 16 a, 16 c would appearilluminated with light 26. As the top layer 24 is configured to changeto a higher transmittance in a region 28 b of the top layer situated onlight-emitting element 16 b in the switched-on state compared to atransmittance in regions 28 a, 28 c of the top layer situated on thelight-emitting elements 16 a, 16 c in the switched-off state, the light26 originating from the lateral light diffusion of the light-emittingelement 16 b is at least partially blocked at the regions 28 a, 28 c ofthe top layer with a lower transmittance. In particular, a substantialpart of the light 26 may be scattered and/or absorbed at the regions 28a, 28 c of the top layer 24, while a substantial part of the light 22may be transmitted through the region 28 b of the top layer 24. Inparticular, the region 28 b of the top layer 24 situated onlight-emitting element 16 b in the switched-on state has translucentproperties.

The switching material is capable of a reversible change intransmittance, such that the transmittance of the regions 28 a-28 c ofthe top layer 24 may be changed or switched according to the choice oflight-emitting elements 16 a-16 c being active. FIGS. 5 and 6 show aside view and top view, respectively, of the lighting device 16 withlight-emitting elements 16 a, 16 c in the switched-on state andlight-emitting element 16 b in the switched-off state. Accordingly, thetop layer 24 changes to a higher transmittance in the regions 28 a, 28 cof the top layer situated on light-emitting elements 16 a, 16 c in theswitched-on state compared to a transmittance in region 28 b of the toplayer situated on light-emitting element 28 b in the switched-off state.

The switching material may in particular comprise at least onethermochromic material such as at least one leuco dye and/or at leastone metal oxide capable of changing the transmittance with temperature.The at least one thermochromic material may be configured to changetransmittance at temperatures corresponding to an operating temperatureof the light-emitting elements 16 a-16 c such that the waste heatproduced by the light-emitting elements 16 a-16 c, and in particularwhite LEDs with phosphor as wavelength conversion element is sufficientto induce the change in transmittance. The switching material is inparticular encapsulated. Encapsulated leuco dyes may for instance beintegrated into the top layer 24 or provided as a coating on the toplayer 24.

As an alternative or in addition, the switching material may comprise atleast one electrochromic material, such as metal oxides, metalhydroxides, viologens, conjugated polymers, metal coordinationcomplexes, metal hexacyanometallates, and/or metal pthalocyanines. Theat least one electrochromic material may be configured to change to ahigher or a lower transmittance when a voltage is applied to the toplayer 24. Voltage can be applied to the regions 28 a-28 c of the toplayer 24 to induce the change in transmittance.

The light-emitting module may further comprise at least onelight-blocking element such as a reflective element arranged between thelight-emitting elements 16 a-16 c to provide additional contrast.

The lighting 14 may be configured as adaptive camera flash light, forinstance in the field of photography, or as automotive lighting and inparticular as an automotive headlight.

What is claimed is:
 1. A lighting device, comprising: a light-emittingmodule with light-emitting elements, wherein the light-emitting elementsare arranged adjacent to each other and are configured to emit lighttowards a light-emitting side, wherein the light-emitting module isconfigured such that the light-emitting elements can be addressed atleast partially independently of each other in that some of thelight-emitting elements may be brought into a switched-on state whileother light-emitting elements may be brought into a switched-off state;and a top layer disposed on the light-emitting module at thelight-emitting side, wherein the top layer comprises a switchingmaterial capable of a reversible change in transmittance for the lightemitted by the light-emitting elements, and wherein the top layer isconfigured to change to a higher transmittance in regions of the toplayer situated on light-emitting elements in the switched-on statecompared to a transmittance in regions of the top layer situated onlight-emitting elements in the switched-off state.
 2. The lightingdevice according to claim 1, wherein the regions of the top layersituated on light-emitting elements in the switched-on state havetranslucent properties.
 3. The lighting device according to claim 1,wherein the switching material comprises at least one thermochromicmaterial.
 4. The lighting device according to claim 3, wherein the atleast one thermochromic material is configured to change transmittanceat temperatures corresponding to an operating temperature of thelight-emitting elements.
 5. The lighting device according to claim 3,wherein the at least one thermochromic material comprises at least oneleuco dye and/or at least one metal oxide.
 6. The lighting deviceaccording to claim 1, wherein the switching material comprises at leastone electrochromic material.
 7. The lighting device according to claim6, wherein the at least one electrochromic material is configured tochange to a higher transmittance when a voltage is applied to the toplayer; or wherein the at least one electrochromic material is configuredto change to a lower transmittance when a voltage is applied to the toplayer.
 8. The lighting device according to claim 6, wherein the at leastone electrochromic material comprises at least one selected from a groupcomprising metal oxides, metal hydroxides, viologens, conjugatedpolymers, metal coordination complexes, metal hexacyanometallates, andmetal pthalocyanines.
 9. The lighting device according to claim 1,wherein the top layer is configured to change transmittance by at least30%, in particular by at least 70%.
 10. The lighting device according toclaim 1, wherein the switching material is capable of a reversiblechange in light scattering for the light emitted by the light-emittingelements and in particular comprises porous silica.
 11. The lightingdevice according to claim 1, wherein the light-emitting module furthercomprises at least one light-blocking element arranged between thelight-emitting elements.
 12. The lighting device according to claim 1being configured as camera flash light or automotive lighting, inparticular as automotive headlight.
 13. A method for producing alighting device, in particular the lighting device according to any ofthe preceding claims, the method comprising: providing a light-emittingmodule by arranging light-emitting elements adjacent to each other suchthat the light-emitting elements emit light towards a light-emittingside, wherein the light-emitting module is configured such that thelight-emitting elements can be addressed independently of each other inthat some of the light-emitting elements may be brought into aswitched-on state while other light-emitting elements may be broughtinto a switched-off state; providing a top layer, wherein the top layercomprises a switching material capable of a reversible change intransmittance for the light emitted by the light-emitting elements; anddisposing the top layer on the light-emitting module at thelight-emitting side, wherein the top layer is configured to change to ahigher transmittance in regions of the top layer situated onlight-emitting elements in the switched-on state compared to atransmittance in regions of the top layer situated on light-emittingelements in the switched-off state.
 14. A method for operating alighting device according to claim 1, the method comprising: bringingsome of the light-emitting elements into a switched-on state andbringing other light-emitting elements into a switched-off state; andchanging the top layer to a higher transmittance in regions of the toplayer situated on light-emitting elements in the switched-on statecompared to a transmittance in regions of the top layer situated onlight-emitting elements in the switched-off state.
 15. Use of a lightingdevice according to claim 1 as camera flash light or in automotivelighting, in particular as automotive headlight.